Create nullable values as strings in config.

- Replace the IsSet bools with string versions of the config values.
  This enables cleaner config files.
- Add FloodProtect config values.
Rewrite inet's flood protection.

- Change the flood protection to something simpler to match simplicity
  of ircd banhammers.
- Update the flood protection to use the new configuration values.
- Fix horrible thread safety bug where the Write() on inet was no longer
  copying the things passed to it.